Burrus et al. U.S. Pat. No. 3,762,281 discloses a type of apparatus for feeding particulate material, for example, activated carbon, from a hopper to provide plug-filler-plug cigarette filters. In such Burrus et al. apparatus an entrance passage of generally circular cross-section is defined by interfitting bottom and top members such that filter wrap may be conformed to partially encircling arrangement with filter plugs spacedly longitudinally secured to the wrap with the remaining peripheries of the plugs and spaces therebetween being enclosed by the upper wall of the entry passage. Such upper entry passage wall, provided by the top member, includes openings and ducts extending therefrom whereby suction pressure may be provided within the entry passage to assist the feeding of material into the spaces between plugs beyond the end of the entry passage, i.e., disposed in a feed station.
In the apparatus feed station, the top member defines a slot of extended longitudinal travel, exposing a succession of plugs and spaces to the discharge outlet of a hopper situated above the top member whereby the hopper contents are applied generally to such plugs and spaces to fill the spaces. Vibration is introduced in the feed station to further facilitate the feeding operation.
Beyond the feed station, the top member slot is terminated and the top passage wall is reconstituted by the top member to provide an exit passage enclosing the plugs and now-filled spaces. In such exit passage, the top member defines transverse grooves which function to trim excess material disposed atop the filter plugs and spaces. While this operation may be assisted by inclusion of a suction aperture within the exit passage, the exit passage nonetheless terminates with the wrap issuing from the top member in open relation to the plugs and filled spaces and a further station is then provided exteriorly of the top member at which station a separate suction device removes material remaining outside the spaces and otherwise interiorly of the wrap. Other structural aspects of this type of apparatus are considered in Burrus et al. U.S. Pat. Nos. 3,772,967 and 3,812,768.
While the foregoing apparatus is suitable for use in feeding free-flowing particulate material, it is not considered to be effective for the feeding of more finely-divided solids, particularly low density materials, such as microporous polyethylene. The latter materials tend to bridge, i.e., agglomerate, even in cavities, openings and passages of relatively wide dimensions. Thus, the aforementioned transverse grooves of the Burrus et al. apparatus are readily clogged by such low density material and thus rendered ineffective to further trim excess material. Further, the introduction of vibration may undesirably result in compacting bridges and hence undesirably reinforcing them.